This is a psychophysical investigation of the mechanisms involved in the perception of spatial patterns by normal, human viewers. The results of recording from single cells in the visual system and the results of recent psychophysical experiments have led to a widely entertained model of pattern vision, often called the multiple-tuned-channel model. The research elaborates the model in three ways. (1) It seeks to define the response ranges or bandwidths of the channels with respect to such dimensions as orientation, spatial frequency, and phase or location. A model is being developed which permits bandwidths to be estimated from a comparison of detection and discrimination data. (2) It further explores the extent to which information (spatial frequency components, contours, etc.) presented at one orientation are processed independently of information presented at other orientations by extending prior researches on gratings to two-dimensional, nonrepetitive stimuli. (3) It explores the nature and extent of inhibitory interaction between channels. Adult subjects with normal vision are used. Stimuli are viewed centrally at photopic luminances. Detection and recognition tasks are used. BIBLIOGRAPHIC REFERENCE: J.P. Thomas (1976). The one-dimensional nature of spatial summation. In V.D. Glezer, ed., Information Processing in the Visual System: Proceedings of the IV Symposium on Sensory System Physiology. Academy of Sciences of the USSR: Leningrad.